Air conditioner and control method thereof

ABSTRACT

Disclosed herein is a water-source heat-pump type air conditioner in which a receiver is connected to a super-cooler or economizer, and a control method of the air conditioner to reduce the quantity of liquid refrigerant collected in the receiver during a cooling/heating overload operation. When a cooling/heating overload operation occurs, an electric expansion valve associated with the super-cooler or the economizer is opened by a predetermined opening degree, to bypass high-pressure liquid refrigerant collected in the receiver, thereby preventing a rapid pressure increase due to a great quantity of liquid refrigerant collected in the receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2010-0011650, filed on Feb. 8, 2010 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments relate to an air conditioner and a control method thereof, which may reduce the quantity of liquid-phase refrigerant collected in a receiver during a cooling/heating overload operation.

2. Description of the Related Art

Generally, although heat naturally moves from a high temperature region to a low temperature region, moving heat from a low temperature region to a high temperature region may require certain external action. This is the principle of a heat pump. A heat-pump type air conditioner performs a cooling or heating operation via reversible switching of a heat transfer mechanism based on a refrigeration cycle consisting of compression-condensation-expansion-evaporation of refrigerant.

Recently, to enhance cooling or heating ability of the heat-pump type air conditioner, a water-source heat-pump type air conditioner has been introduced, in which a receiver is connected to a super-cooler or an economizer. The water-source heat-pump type air conditioner adopts water as a heat source to undergo heat exchange with refrigerant moving in an outdoor heat exchanger. As compared to an outdoor heat exchanger of a general air-source heat-pump type air conditioner, the outdoor heat exchanger of the water-source heat-pump type air conditioner has a smaller volume. Therefore, the water-source heat-pump type air conditioner is provided, at a connection pipe between an outdoor heat exchanger and an indoor heat exchanger, with a receiver to alleviate pressure variation. The receiver is a pressure container serving as a buffer to alleviate discharge pressure variation. Assuming that a great quantity of refrigerant is present in a system, the receiver stores surplus refrigerant and divides the stored refrigerant into gas-phase refrigerant and liquid-phase refrigerant.

The water-source heat-pump type air conditioner also adopts a Pulse Width Modulation (PWM) type variable capacity compressor, to adjust an operation capacity of the compressor. With the PWM type compressor, a system operation capacity is variable according to a duty ratio of a loading time for which refrigerant is compressed to an unloading time for which refrigerant is not compressed.

Upon a cooling or heating operation of the water-source heat-pump type air conditioner, a great quantity of liquid-phase refrigerant may be collected in the receiver if water (heat source) supplied into the outdoor heat exchanger has a high temperature and the system operation capacity is low, i.e. if a cooling/heating overload operation occurs. The great quantity of liquid-phase refrigerant collected in the receiver may reduce a gas refrigerant space, i.e. a buffer space for alleviation of pressure variation, thus causing a rapid pressure increase due to operation capacity variation of the compressor changes or upon loading of the PWM type compressor.

SUMMARY

Therefore, it is an aspect of the embodiment to provide an air conditioner and a control method thereof, which may reduce the quantity of liquid-phase refrigerant collected in a receiver during a cooling/heating overload operation, thus preventing a pressure increase.

Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the embodiments.

In accordance with one aspect of the embodiment, an air conditioner includes a compressor to compress refrigerant, an outdoor heat exchanger to undergo heat exchange between the refrigerant and water, a receiver to store a part of the refrigerant that has undergone heat exchange with the water in the outdoor heat exchanger, and to divide the stored refrigerant into gas refrigerant and liquid refrigerant, a sub heat exchanger to perform super-cooling of the liquid refrigerant separated from the receiver, an electric expansion valve to bypass the liquid refrigerant separated from the receiver, a pressure sensor to sense a pressure of refrigerant discharged from a high-pressure side of the compressor, a temperature sensor to sense a temperature of the outdoor heat exchanger, and a control unit to determine whether or not a cooling/heating overload operation occurs based on an operation capacity of the compressor, the pressure of refrigerant at the high-pressure side and the temperature of the outdoor heat exchanger, and to control an opening degree of the electric expansion valve to reduce the quantity of liquid refrigerant collected in the receiver during the cooling/heating overload operation.

The compressor may be a Pulse Width Modulation (PWM) type compressor, an operation capacity of which is adjusted according to a loading time for which refrigerant is compressed and an unloading time for which compression of refrigerant stops.

The sub heat exchanger may include an economizer or super-cooler.

The electric expansion valve may be an Electronic Expansion Valve (EEV) usable with the economizer or the super-cooler.

The pressure sensor may be installed to a discharge pipe of the compressor to sense a high pressure.

The temperature sensor may be installed to a pipe provided at one side of the outdoor heat exchanger to sense a temperature of a heat exchange location of the refrigerant and the water.

The outdoor heat exchanger may function as a condenser upon a cooling operation, and the temperature sensor may sense an exit temperature of the condenser to measure a temperature of the water.

The outdoor heat exchanger may function as an evaporator upon a heating operation, and the temperature sensor may sense an entrance temperature of the evaporator to measure a temperature of the water.

The control unit may determine occurrence of the cooling overload operation if the operation capacity of the compressor is a predetermined capacity or more upon a cooling operation, the high pressure sensed by the pressure sensor is a first pressure or more and the exit temperature of the condenser sensed by the temperature sensor is a first temperature or more, and may increase the opening degree of the electric expansion valve to bypass the liquid refrigerant inside the receiver to a low-pressure side of the compressor.

The first pressure may be about 30 kg/cm2G. The first temperature may be about 42° C.

The control unit may determine occurrence of the heating overload operation if the operation capacity of the compressor is a predetermined capacity or more upon a heating operation, the high pressure sensed by the pressure sensor is a second pressure or more and the entrance temperature of the evaporator sensed by the temperature sensor is a second temperature or more, and may increase the opening degree of the electric expansion valve to bypass the liquid refrigerant inside the receiver to a low-pressure side of the compressor.

The second pressure may be about 35 kg/cm2G. The second temperature may be about 30° C.

The control unit may counter a bypass operation time for which the liquid refrigerant inside the receiver is bypassed to the low-pressure side through the electric expansion valve having the increased opening degree, and may keep the electric expansion valve at an original opening degree if the bypass operation time exceeds a predetermined time.

The pressure sensor may sense variation of the high pressure caused by bypassing the liquid refrigerant inside the receiver to the low-pressure side through the electric expansion valve having the increased opening degree, and the control unit may keep the electric expansion valve at an original opening degree if the varied pressure is a predetermined pressure or less.

In accordance with another aspect of the embodiment, a control method of an air conditioner, including a compressor to compress refrigerant, an outdoor heat exchanger to perform heat exchange between the refrigerant and water, a receiver to store a part of the heat-exchanged refrigerant to divide the stored refrigerant into gas refrigerant and liquid refrigerant, a sub heat exchanger to perform super-cooling of the liquid refrigerant and an electric expansion valve to bypass the liquid refrigerant, includes sensing a pressure of refrigerant discharged from a high-pressure side of the compressor, sensing a temperature of the outdoor heat exchanger, determining whether or not a cooling/heating overload operation occurs based on an operation capacity of the compressor, the pressure of refrigerant at the high-pressure side and the temperature of the outdoor heat exchanger, and bypassing the liquid refrigerant inside the receiver to reduce the quantity of liquid refrigerant collected in the receiver during the cooling/heating overload operation.

The occurrence of the cooling overload operation may be determined if the operation capacity of the compressor is a predetermined capacity or more upon a cooling operation, the pressure of refrigerant at the high-pressure side of the compressor is a first pressure or more and the temperature of the outdoor heat exchanger is a first temperature or more.

The occurrence of the heating overload operation may be determined if the operation capacity of the compressor is a predetermined capacity or more upon a heating operation, the pressure of refrigerant at the high-pressure side of the compressor is a second pressure or more and the temperature of the outdoor heat exchanger is a second temperature or more.

The bypass of the liquid refrigerant inside the receiver may include opening the electric expansion valve by a predetermined opening degree to allow the liquid refrigerant inside the receiver to be bypassed to a low-pressure side of the compressor.

The control method may further include countering a bypass operation time for which the liquid refrigerant inside the receiver is bypassed to the low-pressure side through the electric expansion valve having a predetermined opening degree, and keeping the electric expansion valve at an original opening degree if the bypass operation time exceeds a predetermined time.

The control method may further include sensing pressure variation of refrigerant at the high-pressure side caused by bypassing the liquid refrigerant inside the receiver to the low-pressure side through the electric expansion valve having a predetermined opening degree, and keeping the electric expansion valve at an original opening degree if the sensed pressure at the high-pressure side is a predetermined pressure or less.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the embodiments will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a diagram illustrating a water-source heat-pump type air conditioner according to an embodiment;

FIG. 2 is a diagram illustrating the flow of refrigerant during a heating operation of the air conditioner illustrated in FIG. 1;

FIG. 3 is a diagram illustrating the flow of refrigerant during a cooling operation of the air conditioner illustrated in FIG. 1;

FIG. 4 is a diagram illustrating a water-source heat-pump type air conditioner according to another embodiment;

FIG. 5 is a diagram illustrating the flow of refrigerant during a heating operation of the air conditioner illustrated in FIG. 4;

FIG. 6 is a diagram illustrating the flow of refrigerant during a cooling operation of the air conditioner illustrated in FIG. 4;

FIG. 7 is a graph illustrating operation capacity variation upon loading and unloading of a PWM type compressor usable with the water-source heat-pump type air conditioner according to the embodiments;

FIG. 8 is a control block diagram of the water-source heat-pump type air conditioner according to the embodiments of FIGS. 1 and 4;

FIG. 9 is a flow chart illustrating a control method of an air conditioner with respect to a cooling operation according to an embodiment;

FIG. 10 is a flow chart illustrating a control method of an air conditioner with respect to a heating operation according to an embodiment;

FIG. 11 is a flow chart illustrating a control method of an air conditioner with respect to a cooling operation according to an embodiment;

FIG. 12 is a flow chart illustrating a control method of an air conditioner with respect to a heating operation according to an embodiment;

FIG. 13 is a diagram illustrating a ground-source heat-pump type air conditioner according to an embodiment; and

FIG. 14 is a diagram illustrating a ground-source heat-pump type air conditioner according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 is a diagram illustrating a water-source heat-pump type air conditioner according to an embodiment.

In FIG. 1, the water-source heat-pump type air conditioner according to the embodiment includes a single outdoor unit 100, and a plurality of indoor units 200 arranged in parallel to the outdoor unit 100. A water heat source 300 (i.e. a cooling tower) is connected to the outdoor unit 100 and is used to supply water (heat source water) into the outdoor unit 100 (more particularly, an outdoor heat exchanger).

The outdoor unit 100 includes a compressor 10, oil separator 25, 4-way valve 30, outdoor heat exchanger 40, outdoor expansion valve 45, receiver 50, economizer 60, electric expansion valve 62, solenoid valve 64, injection pipe 66, and accumulator 70.

The compressor 10 has two suction holes 11 and 12 and a single discharge hole 13. The two suction holes 11 and 12 include a low-pressure suction hole 11 connected to a low-pressure compressing chamber and a medium-pressure suction hole 12 connected to a medium-pressure compressing chamber. Accordingly, the compressor 10 is of a dual stage compression type, which compresses low-temperature and low-pressure gas-phase refrigerant suctioned through the low-pressure suction hole 11 thus discharging high-temperature and high-pressure gas-phase refrigerant through the discharge hole 13, a part of the refrigerant bypassed from the economizer 60 being introduced into the compressor 10 through the medium-pressure suction hole 12 during compression.

The oil separator 25 serves to separate oil included in the refrigerant discharged from the compressor 10.

The 4-way valve 30 serves to switch the flow of the refrigerant discharged from the compressor 10 according to an operation mode (i.e. a cooling or heating operation mode). The 4-way valve 30 includes a first port 31 connected to the oil separator 25 provided at a discharge side of the compressor 10, a second port 32 connected to the outdoor heat exchanger 40, a third port 33 connected to the indoor units 200, and a fourth port 34 connected to the accumulator 70 provided at a suction side of the compressor 10.

The outdoor heat exchanger 40 serves as an evaporator in a heating operation mode to evaporate low-temperature and low-pressure liquid-phase refrigerant into gas-phase refrigerant, or a condenser in a cooling operation mode to condense high-temperature and high-pressure gas-phase refrigerant into normal-temperature and high-pressure liquid-phase refrigerant. That is, the outdoor heat exchanger 40 is a main heat exchanger to undergo heat exchange between refrigerant and water (heat source water) supplied from the water heat source 300 in response to enthalpy variation.

The outdoor expansion valve 45 is an Electronic Expansion Valve (EEV) installed to a pipe between the outdoor heat exchanger 40 and the receiver 50, which serves to expand refrigerant thus reducing pressure of the refrigerant.

The receiver 50 is installed to a pipe between the outdoor heat exchanger 40 and the economizer 60 and is configured to store a part of the refrigerant circulating between the outdoor heat exchanger 40 and the indoor units 200. Specifically, the receiver 50 is a pressure container serving as a buffer to alleviate discharge pressure variation. If a great quantity of refrigerant is present in a system, the receiver 50 functions to store surplus refrigerant and to divide the stored refrigerant into gas-phase refrigerant (in brief, gas refrigerant) and liquid-phase refrigerant (in brief, liquid refrigerant).

The economizer 60 is installed to a pipe between the receiver 50 and the indoor units 200 and serves as a sub heat exchanger in which a part of the liquid refrigerant discharged from the receiver 50 undergoes heat exchange with the remaining liquid refrigerant expanded by the electric expansion valve 62 after being discharged from the receiver 50, thus achieving a super-cooling degree of the refrigerant. The expanded liquid refrigerant, having passed through the electric expansion valve 62, acquires heat while passing through the economizer 60, thereby being changed into gas refrigerant.

The electric expansion valve 62 is an electronic expansion valve to expand a part of the refrigerant flowing from the receiver 50 to the economizer 60, or a part of the refrigerant flowing from one side of the economizer 60 to the other side of the economizer 60. Thus, the economizer 60 receives the expanded refrigerant having passed through the electric expansion valve 62. The economizer 60 and the electric expansion valve 62 constitute a gas-liquid separator installed to a liquid pipe between the indoor units 200 and the outdoor heat exchanger 40, thus serving to separate gas refrigerant from the liquid refrigerant flowing from the indoor units 200 to the outdoor heat exchanger 40 during a heating operation.

The solenoid valve 64 is connected to a low-pressure pipe between the economizer 60 and the accumulator 70 and is opened or closed to introduce the heat-exchanged refrigerant from the economizer 60 into the accumulator 70 or the medium-pressure suction hole 12 of the compressor 10. When the solenoid valve 64 is opened, the refrigerant discharged from the economizer 60 is introduced into the accumulator 70 having a relatively low pressure. When the solenoid valve 64 is closed, the refrigerant discharged from the economizer 60 is introduced into the injection pipe 66 connected to the medium-pressure suction hole 12 of the compressor 10 having a relative high pressure.

The injection pipe 66 is branched from the low-pressure pipe between the economizer 66 and the accumulator 70 and is connected to the medium-pressure suction hole 12 of the compressor 10. Therefore, when the solenoid valve 64 is opened, the gas refrigerant discharged from the economizer 60 is not allowed to move into the injection pipe 66 connected to the medium-pressure suction hole 12 of the relatively high-pressure compressor 10 and thus, is introduced into the relatively low-pressure accumulator 70. On the other hand, when the solenoid valve 64 is closed, the gas refrigerant discharged from the economizer 60 moves to the medium-pressure suction hole 12 of the compressor 10 by passing through the injection pipe 66.

The accumulator 70 serves to temporarily store the refrigerant moved from the outdoor heat exchanger 40 or the indoor units 200 before the refrigerant is introduced into the suction hole of the compressor 10. The refrigerant is divided into gas refrigerant and liquid refrigerant while staying in the accumulator 70. The gas refrigerant separated from the accumulator 70 is suctioned into the low-pressure suction hole 11 of the compressor 10.

The outdoor unit 100 further includes a pressure sensor 82 and a temperature sensor 84.

The pressure sensor 82 is installed to a pipe connected to the discharge hole 13 of the compressor 10. More particularly, the pressure sensor 82 is installed to a high-pressure pipe through which the refrigerant is discharged from the compressor 10, thus functioning to sense a pressure of the refrigerant at a high-pressure side of the compressor 10.

The temperature sensor 84 is installed to a pipe provided at one side of the outdoor heat exchanger 40 and serves to sense a temperature of a heat exchange region between water (heat source water) and the refrigerant. The temperature sensor 84 senses an exit temperature of the outdoor heat exchanger 40, i.e. an exit temperature of the condenser during a cooling operation, and senses an entrance temperature of the outdoor heat exchanger 40, i.e. an entrance temperature of the evaporator during a heating operation, thereby measuring a temperature of the water (heat source water).

FIG. 2 is a diagram illustrating the flow of refrigerant during a cooling operation of the air conditioner illustrated in FIG. 1, and FIG. 3 is a diagram illustrating the flow of refrigerant during a heating operation of the air conditioner illustrated in FIG. 1.

In FIG. 2, the refrigerant creates a refrigeration cycle for a heating operation in the sequence of the compressor 10→the 4-way valve 30→the indoor units 200→the economizer 60→the receiver 50→the outdoor heat exchanger 40→the 4-way valve 30→the accumulator 70→the compressor 10.

In FIG. 3, the refrigerant creates a refrigeration cycle for a cooling operation in the sequence of the compressor 10→the 4-way valve 30→the outdoor heat exchanger 40→the receiver 50→the economizer 60→the indoor units 200→the 4-way valve 30→the accumulator 70→the compressor 10.

FIG. 4 is a diagram illustrating a water-source heat-pump type air conditioner according to another embodiment. The same configurations as those of FIG. 1 will be designated by the same reference numerals and terms.

In FIG. 4, the water-source heat-pump type air conditioner according to the present embodiment, similar to FIG. 1, includes a single outdoor unit 400 and a plurality of indoor units 200 arranged in parallel to the outdoor unit 400. The water heat source 300 (i.e. a cooling tower) is connected to the outdoor unit 400 and is used to supply water (heat source water) into the outdoor unit 400 (more particularly, an outdoor heat exchanger).

The outdoor unit 400 includes a compressor 20, oil separator 25, 4-way valve 30, outdoor heat exchanger 40, outdoor expansion valve 45, receiver 50, super-cooler 90, electric expansion valve 92 and accumulator 70.

The outdoor unit 400 of FIG. 4 has the same configuration as that of the outdoor unit 100 of FIG. 1 except for the compressor 20, super-cooler 90 and electric expansion valve 92 and thus, a repeated description thereof will be omitted as possible.

The compressor 20, differently from the compressor 10 provided in the outdoor unit 100 of FIG. 1, has a single suction hole 21 and a single discharge hole 23. Thus, the compressor 20 serves to compress low-temperature and low-pressure gas refrigerant suctioned through the suction hole 21 thus discharging high-temperature and high-pressure gas refrigerant through the discharge hole 23.

The super-cooler 90, similar to the economizer 60 provided in the outdoor unit 100 of FIG. 1, is installed to a pipe between the receiver 50 and the indoor units 200 and serves as a sub heat exchanger in which a part of the liquid refrigerant discharged from the receiver 50 undergoes heat exchange with the remaining liquid refrigerant expanded by the electric expansion valve 92 after being discharged from the receiver 50, thus achieving a super-cooling degree of the refrigerant. The expanded refrigerant, having passed through the electric expansion valve 92, acquires heat while passing through the super-cooler 90, thereby being changed into gas refrigerant.

The electric expansion valve 92 is an electronic expansion valve to expand a part of the refrigerant flowing from the receiver 50 to the super-cooler 90, or a part of the refrigerant flowing from one side of the super-cooler 90 to the other side of the super-cooler 90. The refrigerant expanded by the electric expansion valve 92 is introduced into the super-cooler 90. The super-cooler 90 and the electric expansion valve 92 constitute a gas-liquid separator installed to a liquid pipe between the indoor units 200 and the outdoor heat exchanger 40, thus serving to separate gas refrigerant from the refrigerant flowing from the indoor units 200 to the outdoor heat exchanger 40 during a heating operation.

Comparing the super-cooler 90 of FIG. 4 with the economizer 60 of FIG. 1, the super-cooler 90 has the same refrigerant flow as that of the economizer 60 when the solenoid valve 64 of FIG. 1 is closed.

FIG. 5 is a diagram illustrating the flow of refrigerant during a heating operation of the air conditioner illustrated in FIG. 4, and FIG. 6 is a diagram illustrating the flow of refrigerant during a cooling operation of the air conditioner illustrated in FIG. 4.

In FIG. 5, the refrigerant creates a refrigeration cycle for a heating operation in the sequence of the compressor 20→the 4-way valve 30→the indoor units 200 the super-cooler 90→the receiver 50→the outdoor heat exchanger 40→the 4-way valve 30→the accumulator 70→the compressor 20.

In FIG. 6, the refrigerant creates a refrigeration cycle for a cooling operation in the sequence of the compressor 20→the 4-way valve 30→the outdoor heat exchanger 40→the receiver 50→the super-cooler 90→the indoor units 200→the 4-way valve 30→the accumulator 70→the compressor 20.

Both the compressor 10 of FIG. 1 and the compressor 20 of FIG. 4 are Pulse Width Modulation (PWM) type variable capacity compressors, as illustrated in FIG. 7.

FIG. 7 is a graph illustrating operation capacity variation upon loading and unloading of the PWM type compressor usable with the water-source heat-pump type air conditioner according to the embodiments.

In FIG. 7, “loading” refers to a state in which refrigerant is compressed in the PWM type compressor 10 or 20 and the compressed refrigerant is discharged from the PWM type compressor 10 or 20. The compressor 10 or 20 has an operation capacity of 100% upon loading.

On the other hand, “unloading” refers to a state in which the PWM type compressor 10 or 20 stops compression of refrigerant and discharges no refrigerant. The compressor 10 or 20 has an operation capacity of 0% upon unloading.

Accordingly, the compressor 10 or 20 entails a pressure increase upon loading and also, entails a pressure decrease upon unloading.

With the compressor 10 or 20, a system operation capacity is variable according to a duty ratio of a loading time for which compressed refrigerant is discharged to an unloading time for which discharge of refrigerant stops.

In one example, assuming that a cycle of the compressor 10 or 20 is 10 seconds and a loading operation to compress refrigerant is performed for a predetermined time (2 seconds) and an unloading operation is performed for the remaining time (8 seconds), the system operation capacity is 20%.

In another example, assuming that a cycle of the compressor 10 or 20 is 10 seconds and a loading operation to compress refrigerant is performed for a predetermined time (5 seconds) and an unloading operation is performed for the remaining time (5 seconds), the system operation capacity is 50%.

As described above, the operation capacity of the variable capacity compressor 10 or 20 may be adjusted by determining the loading time and unloading time of the compressor 10 or 20 according to required cooling and heating abilities of the indoor units 200.

FIG. 8 is a control block diagram of the water-source heat-pump type air conditioner according to the embodiments of FIGS. 1 and 4.

In FIG. 8, the water-source heat-pump type air conditioner according to the embodiments includes a control unit 86, which adopts a microcomputer and peripheral circuits to control respective constituent elements of the air conditioner.

Provided at an input side of the control unit 86 are the pressure sensor 82, the temperature sensor 84 and an input unit 88 to receive a user operation command.

An output side of the control unit 86 is electrically connected to the compressor 10 or 20, 4-way valve 30, outdoor expansion valve 45, electric expansion valve 62 associated with the economizer 60, solenoid valve 64, and an electric expansion valve 92 associated with the super-cooler 90.

The control unit 86 operates the 4-way valve 30 according to a cooling or heating operation required by the indoor units 200, thus switching the flow of refrigerant between the heating operation refrigeration cycle of FIGS. 2 and 5 and the cooling operation refrigeration cycle of FIGS. 3 and 6.

The control unit 86 determines whether a cooling/heating overload operation occurs based on sensed values of the pressure sensor 82 and temperature sensor 84 and the operation capacity of the compressor 10 or 20 during a cooling or heating operation. If the cooling/heating overload operation is determined, an opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is adjusted to bypass the high-pressure liquid refrigerant to a low-pressure side of the compressor 10 or 20, thus reducing the quantity of liquid refrigerant collected in the receiver 50.

For example, during a normal cooling/heating operation, the electric expansion valve 62 associated with the economizer 60 and the electric expansion valve 92 associated with the super-cooler 90 respectively have an opening degree of about 100˜300 steps, thus serving to provide the economizer 60 and the super-cooler 90 with low-temperature refrigerant, respectively. On the other hand, during a cooling/heating overload operation, the electric expansion valves 62 and 92 respectively have an increased opening degree of about 480 steps, thus serving to bypass a great quantity of liquid refrigerant collected in the receiver 50 to the low-pressure side of the compressor 10 or 20.

More specifically, the control unit 86 determines occurrence of a cooling overload operation if the operation capacity of the compressor 10 or 20 is 15% or more of a total operation capacity during a cooling operation, a pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined first pressure or more, and an exit temperature of the condenser sensed by the temperature sensor 84 is a predetermined first temperature or more. Accordingly, the control unit 86 opens the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 by a predetermined opening degree (about 480 steps), to reduce the quantity of liquid refrigerant collected in the receiver 50, thus preventing a pressure increase. In this case, assuming that the refrigerant is R410A, the predetermined first pressure is 30 kg/cm²G and the predetermined first temperature is 42° C.

In addition, the control unit 86 determines occurrence of a heating overload operation if the operation capacity of the compressor 10 or 20 is 15% or more of a total operation capacity during a heating operation, a pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined second pressure or more, and an entrance temperature of the evaporator sensed by the temperature sensor 84 is a predetermined second temperature or more. Accordingly, the control unit 86 opens the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 by a predetermined opening degree (about 480 steps), to reduce the quantity of liquid refrigerant collected in the receiver 50, thus preventing a pressure increase. In this case, assuming that the refrigerant is R410A, the predetermined second pressure is 35 kg/cm²G and the predetermined second temperature is 30° C.

Here, the operation to open the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 by a predetermined opening degree (about 480 steps) based on the determination of a cooling/heating overload operation is a bypass operation. After performing the bypass operation for a predetermined time (about 3 minutes), the control unit 86 returns the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 from the predetermined opening degree (about 480 steps) to the opening degree of a normal operation mode (about 100˜300 steps), to perform a basic operation to provide the economizer 60 and the super-cooler 90, respectively, with low-temperature refrigerant.

To allow the control unit 86 to return the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90, respectively, to the normal opening degree (about 100˜300 steps), in addition to confirming implementation of the bypass operation for the predetermined time (about 3 minutes), the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 may be sensed by the pressure sensor 82. Even when the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is lowered to a predetermined third or fourth pressure or less, the basic operation to provide the economizer 60 and the super-cooler 90 with low-temperature refrigerant may be performed by returning the predetermined opening degree (about 480 steps) of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90, respectively, to the normal opening degree (about 100˜300 steps). In this case, the predetermined third pressure may be 25 kg/cm²G or less lower than the pressure value of 30 kg/cm²G with respect to a cooling operation, and the predetermined fourth pressure may be 30 kg/cm²G) or less lower than the pressure value of 35 kg/cm²G with respect to a heating operation according to an embodiment.

Hereinafter, operations and effects of the air conditioner having the above described configuration and a control method thereof will be described.

FIG. 9 is a flow chart illustrating a control method of an air conditioner with respect to a cooling operation according to an embodiment.

In FIG. 9, the control unit 86 receives a required cooling ability from the indoor unit 200 (operation 500) and switches the 4-way valve 30 to change the flow of refrigerant as illustrated in FIGS. 3 and 6, thus initiating a cooling operation (operation 502).

Then, the control unit 86 supplies power to the compressor 10 or 20 and determines a loading time for which refrigerant is compressed and discharged and an unloading time for which discharge of refrigerant stops according to the required cooling ability as illustrated in FIG. 7, thus adjusting the operation capacity of the compressor 10 or 20 (operation 504).

Thereafter, the control unit 86 determines whether the operation capacity of the compressor 10 or 20 is a predetermined operation capacity (about 15%) or more of a total operation capacity (operation 506). If the operation capacity of the compressor 10 or 20 is the predetermined operation capacity (about 15%) or more, the control unit 86 determines that a system operation capacity is low.

Under the assumption of the low system operation capacity, the control unit 86 senses a pressure of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 installed to the pipe provided at the discharge hole 13 of the compressor 10 or 20 (operation 508).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined first pressure or more (operation 510). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is the predetermined first pressure or more, the control unit 86 senses an exit temperature of the outdoor heat exchanger 40 in which the refrigerant undergoes heat exchange with water (heat source water), i.e. an exit temperature of the condenser by use of the temperature sensor 84 (operation 512).

The control unit 86 determines whether the exit temperature of the condenser sensed by the temperature sensor 84 is the predetermined first temperature or more (operation 514). If the exit temperature of the condenser is the predetermined first temperature or more, the control unit 86 determines the occurrence of a cooling overload operation.

If water (heat source water) supplied into the outdoor heat exchanger 40 has a high temperature and a system operation capacity is low during the cooling overload operation, a great quantity of refrigerant is collected in the receiver 50 and the compressor 10 or 20 has an increased discharge pressure (condensation pressure). When a great quantity of refrigerant is collected in the receiver 50 during the cooling overload operation, the receiver 50 serving as a buffer to alleviate pressure variation has a reduced gas refrigerant space. Accordingly, as a buffer space for alleviation of pressure variation is reduced due to operation capacity variation of the compressor 10 or 20 or upon loading of the compressor 10 or 20, or as the receiver 50 is full of refrigerant, an instantaneous pressure increase may occur.

Accordingly, once the cooling overload operation is determined, the control unit 86 increases the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 to a predetermined value (about 480 steps) (operation 516), to perform a bypass operation to bypass high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20, thus reducing the quantity of liquid refrigerant collected in the receiver 50 (operation 518).

Once the quantity of liquid refrigerant collected in the receiver 50 is reduced by the bypass operation, the control unit 86 determines whether the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has proceeded for a predetermined time (about 3 minutes) (operation 520).

If it is determined based on a result of operation 520 that the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has not proceeded for the predetermined time, the control method is fed back to operation 518 to continuously perform the bypass operation.

On the contrary, if it is determined based on a result of operation 520 that the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has proceeded for the predetermined time, the opening degree (about 480 steps) of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is changed to the opening degree of a normal operation mode (about 100˜300 steps) (operation 522) and a cooling operation is performed (operation 524).

In the meantime, if it is determined based on a result of operation 506 that the operation capacity of the compressor 10 or 20 is not the predetermined operation capacity (about 15%) or more of a total operation capacity, the control method proceeds to operation 522 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 524).

Also, if it is determined based on a result of operation 510 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is the predetermined first pressure or more, the control method proceeds to operation 522 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 524).

If it is determined based on a result of operation 514 that the exit temperature of the condenser is not the predetermined first temperature or more, the control method proceeds to operation 522 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 524).

FIG. 10 is a flow chart illustrating a control method of an air conditioner with respect to a heating operation according to an embodiment.

In FIG. 10, the control unit 86 receives a required heating ability from the indoor unit 200 (operation 600) and switches the 4-way valve 30 to change the flow of refrigerant as illustrated in FIGS. 2 and 5, thus initiating a heating operation (operation 602).

Then, the control unit 86 supplies power to the compressor 10 or 20 and determines a loading time for which refrigerant is compressed and discharged and an unloading time for which discharge of refrigerant stops according to the required heating ability as illustrated in FIG. 7, thus adjusting the operation capacity of the compressor 10 or 20 (operation 604).

Thereafter, the control unit 86 determines whether the operation capacity of the compressor 10 or 20 is a predetermined operation capacity (about 15%) or more of a total operation capacity (operation 606). If the operation capacity of the compressor 10 or 20 is the predetermined operation capacity (about 15%) or more, the control unit 86 determines that a system operation capacity is low.

Under the assumption of the low system operation capacity, the control unit 86 senses a pressure of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 installed to the pipe provided at the discharge hole 13 of the compressor 10 or 20 (operation 608).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined second pressure or more (operation 610). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is the predetermined second pressure or more, the control unit 86 senses an entrance temperature of the outdoor heat exchanger 40 in which the refrigerant undergoes heat exchange with water (heat source water), i.e. an entrance temperature of the evaporator by use of the temperature sensor 84 (operation 612).

The control unit 86 determines whether the entrance temperature of the evaporator sensed by the temperature sensor 84 is the predetermined second temperature or more (operation 614). If the entrance temperature of the evaporator is the predetermined second temperature or more, the control unit 86 determines the occurrence of a heating overload operation.

If water (heat source water) supplied into the outdoor heat exchanger 40 has a high temperature and a system operation capacity is low during the heating overload operation, similar to the cooling overload operation, a great quantity of refrigerant is collected in the receiver 50 and the compressor 10 or 20 has an increased discharge pressure (condensation pressure). When a great quantity of refrigerant is collected in the receiver 50 during the heating overload operation, the receiver 50 serving as a buffer to alleviate pressure variation has a reduced gas refrigerant space. Accordingly, as a buffer space for alleviation of pressure variation is reduced due to operation capacity variation of the compressor 10 or 20 or upon loading of the compressor 10 or 20, or as the receiver 50 is full of refrigerant, an instantaneous pressure increase may occur.

Accordingly, once the heating overload operation is determined, the control unit 86 increases the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 to a predetermined value (about 480 steps) (operation 616), to perform a bypass operation to bypass high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20, thus reducing the quantity of liquid refrigerant collected in the receiver 50 (operation 618).

Once the quantity of liquid refrigerant collected in the receiver 50 is reduced by the bypass operation, the control unit 86 determines whether the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has proceeded for a predetermined time (about 3 minutes) (operation 620).

If it is determined based on a result of operation 620 that the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has not proceeded for the predetermined time, the control method is fed back to operation 618 to continuously perform the bypass operation.

If it is determined based on a result of operation 620 that the bypass operation to bypass the high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 has proceeded for the predetermined time, the opening degree (about 480 steps) of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is changed to the opening degree of a normal operation mode (about 100˜300 steps) (operation 622) and a heating operation is performed (operation 624).

In operation 624, if it is determined based on a result of operation 606 that the operation capacity of the compressor 10 or 20 is not the predetermined operation capacity (about 15%) or more of a total operation capacity, the control method proceeds to operation 622 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 624).

Also, if it is determined based on a result of operation 610 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is not the predetermined second pressure or more, the control method proceeds to operation 622 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 624).

If it is determined based on a result of operation 614 that the entrance temperature of the evaporator is not the predetermined second temperature or more, the control method proceeds to operation 622 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 624).

FIG. 11 is a flow chart illustrating a control method of an air conditioner with respect to a cooling operation according to an embodiment. In the following description, a repeated description of the same configuration as that of FIG. 9 will be omitted as possible.

In FIG. 11, the control unit 86 receives a required cooling ability from the indoor unit 200 (operation 700) and switches the 4-way valve 30 to change the flow of refrigerant as illustrated in FIGS. 3 and 6, thus initiating a cooling operation (operation 702).

Then, the control unit 86, as illustrated in FIG. 7, adjusts the operation capacity of the compressor 10 or 20 according to the required cooling ability (operation 704).

Thereafter, the control unit 86 determines whether the operation capacity of the compressor 10 or 20 is a predetermined operation capacity (about 15%) or more of a total operation capacity (operation 706). If the operation capacity of the compressor 10 or 20 is the predetermined operation capacity (about 15%) or more, the control unit 86 determines that a system operation capacity is low.

Under the assumption of the low system operation capacity, the control unit 86 senses a pressure of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 (operation 708).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined first pressure or more (operation 710). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is the predetermined first pressure or more, the control unit 86 senses an exit temperature of the outdoor heat exchanger 40, i.e. an exit temperature of the condenser by use of the temperature sensor 84 (operation 712).

The control unit 86 determines whether or not the exit temperature of the condenser sensed by the temperature sensor 84 is a predetermined first temperature or more (operation 714). If the exit temperature of the condenser is the predetermined first temperature or more, the control unit 86 determines the occurrence of a cooling overload operation.

Accordingly, once the cooling overload operation is determined, the control unit 86 increases the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 to a predetermined value (about 480 steps) (operation 716), thereby performing a bypass operation to bypass high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 to reduce the quantity of liquid refrigerant collected in the receiver 50 (operation 718).

Once the quantity of liquid refrigerant collected in the receiver 50 is reduced by the bypass operation, the control unit 86 senses pressure variation of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 (operation 720).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is lowered to a predetermined third pressure or less (operation 722). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is not lowered to the third pressure or less, the control method is fed back to operation 718 to continuously perform the bypass operation.

On the contrary, if it is determined based on a result of operation 722 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is lowered to the third pressure or less owing to the bypass operation to bypass the liquid refrigerant collected in the receiver 50 to the low-pressure side of the compressor 10 or 20, the opening degree (about 480 steps) of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is changed to the opening degree of a normal operation mode (about 100˜300 steps) (operation 724) and a cooling operation is performed (operation 726).

In the meantime, if it is determined based on a result of operation 706 that the operation capacity of the compressor 10 or 20 is not the predetermined operation capacity (about 15%) or more of a total operation capacity, the control method proceeds to operation 724 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 726).

Also, if it is determined based on a result of operation 710 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is not the predetermined first pressure or more, the control method proceeds to operation 724 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 726).

If it is determined based on a result of operation 714 that the exit temperature of the condenser is not the predetermined first temperature or more, the control method proceeds to operation 724 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a cooling operation is performed (operation 726).

FIG. 12 is a flow chart illustrating a control method of an air conditioner with respect to a heating operation according to an embodiment. In the following description, a repeated description of the same configuration as that of FIG. 10 will be omitted as possible.

In FIG. 12, the control unit 86 receives a required heating ability from the indoor unit 200 (operation 800) and switches the 4-way valve 30 to change the flow of refrigerant as illustrated in FIGS. 2 and 5, thus initiating a heating operation (operation 802).

Then, the control unit 86, as illustrated in FIG. 7, adjusts the operation capacity of the compressor 10 or 20 according to the required heating ability (operation 804).

Thereafter, the control unit 86 determines whether the operation capacity of the compressor 10 or 20 is a predetermined operation capacity (about 15%) or more of a total operation capacity (operation 806). If the operation capacity of the compressor 10 or 20 is the predetermined operation capacity (about 15%) or more, the control unit 86 determines that a system operation capacity is low.

Under the assumption of the low system operation capacity, the control unit 86 senses a pressure of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 (operation 808).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is a predetermined second pressure or more (operation 810). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is the predetermined second pressure or more, the control unit 86 senses an entrance temperature of the outdoor heat exchanger 40, i.e. an entrance temperature of the evaporator by use of the temperature sensor 84 (operation 812).

The control unit 86 determines whether the entrance temperature of the evaporator sensed by the temperature sensor 84 is a predetermined second temperature or more (operation 814). If the entrance temperature of the evaporator is the predetermined second temperature or more, the control unit 86 determines the occurrence of a heating overload operation.

Accordingly, once the heating overload operation is determined, the control unit 86 increases the opening degree of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 to a predetermined value (about 480 steps) (operation 816), thereby performing a bypass operation to bypass high-pressure liquid refrigerant to the low-pressure side of the compressor 10 or 20 to reduce the quantity of liquid refrigerant collected in the receiver 50 (operation 818).

Once the quantity of liquid refrigerant collected in the receiver 50 is reduced by the bypass operation, the control unit 86 senses pressure variation of the refrigerant discharged from the high-pressure side of the compressor 10 or 20 by use of the pressure sensor 82 (operation 820).

The control unit 86 determines whether the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 sensed by the pressure sensor 82 is lowered to a predetermined fourth pressure or less (operation 822). If the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is not lowered to the fourth pressure or less, the control method is fed back to operation 818 to continuously perform the bypass operation.

On the contrary, if it is determined based on a result of operation 822 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is lowered to the fourth pressure or less owing to the bypass operation to bypass the liquid refrigerant collected in the receiver 50 to the low-pressure side of the compressor 10 or 20, the opening degree (about 480 steps) of the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is changed to the opening degree of a normal operation mode (about 100˜300 steps) (operation 824) and a heating operation is performed (operation 826).

In the meantime, if it is determined based on a result of operation 806 that the operation capacity of the compressor 10 or 20 is not the predetermined operation capacity (about 15%) or more of a total operation capacity, the control method proceeds to operation 824 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 826).

Also, if it is determined based on a result of operation 810 that the pressure of the refrigerant at the high-pressure side of the compressor 10 or 20 is not the predetermined first pressure or more, the control method proceeds to operation 824 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 826).

If it is determined based on a result of operation 814 that the exit temperature of the condenser is not the predetermined second temperature or more, the control method proceeds to operation 824 in which the electric expansion valve 62 associated with the economizer 60 or the electric expansion valve 92 associated with the super-cooler 90 is kept at the opening degree of a normal operation mode (about 100˜300 steps) and a heating operation is performed (operation 826).

In the meantime, although the above described embodiments describe the heat-pump type air conditioner using the water heat source 300 in which refrigerant passing through the outdoor heat exchanger 40 undergoes heat exchange with water (heat source water) by way of example, embodiments are not limited thereto, and the same aspects and effects will be accomplished even by a ground-source heat-pump type air conditioner in which refrigerant passing through the outdoor heat exchanger 40 undergoes heat exchange using ground heat generated by a ground heat source 350.

FIGS. 13 and 14 illustrate an exemplary ground-source heat-pump type air conditioner.

FIG. 13 is a diagram illustrating a ground-source heat-pump type air conditioner according to an embodiment.

In FIG. 13, the ground-source heat-pump type air conditioner according to the embodiment includes the single outdoor unit 100, and the plurality of indoor units 200 arranged in parallel to the outdoor unit 100. A ground heat source 350 is connected to the outdoor unit 100 and is used to supply ground heat to the outdoor unit 100 (more particularly, an outdoor heat exchanger).

The ground-source heat-pump type air conditioner of FIG. 13 has the same configuration as the water-source heat-pump type air conditioner of FIG. 1 except that refrigerant passing through the outdoor heat exchanger 40 undergoes heat exchange using ground heat and thus, a repeated description of the same configuration as that of FIG. 1 will be omitted.

FIG. 14 is a diagram illustrating a ground-source heat-pump type air conditioner according to an embodiment.

In FIG. 14, the ground-source heat-pump type air conditioner according to the embodiment includes the single outdoor unit 400, and the plurality of indoor units 200 arranged in parallel to the outdoor unit 400. The ground heat source 350 is connected to the outdoor unit 400 and is used to supply ground heat to the outdoor unit 400 (more particularly, an outdoor heat exchanger).

The ground-source heat-pump type air conditioner of FIG. 14 has the same configuration as the water-source heat-pump type air conditioner of FIG. 4 except that refrigerant passing through the outdoor heat exchanger 40 undergoes heat exchange using ground heat and thus, a repeated description of the same configuration as that of FIG. 4 will be omitted.

As apparent from the above description, according to an embodiment, when a cooling/heating overload operation occurs, an electric expansion valve associated with a super-cooler or economizer is opened at a predetermined opening degree, to bypass high-temperature and high-pressure liquid refrigerant collected in a receiver connected to the super-cooler or economizer, thereby preventing a rapid pressure increase.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit thereof, the scope of which is defined in the claims and their equivalents. 

1. An air conditioner, comprising: a compressor to compress refrigerant; an outdoor heat exchanger to undergo heat exchange between the refrigerant and water; a receiver to store a part of the refrigerant that has undergone heat exchange with the water in the outdoor heat exchanger, and to divide the stored refrigerant into gas, refrigerant and liquid refrigerant; a sub heat exchanger to perform super-cooling of the liquid refrigerant separated from the receiver; an electric expansion valve to bypass the liquid refrigerant separated from the receiver; a pressure sensor to sense a pressure of refrigerant discharged from a high-pressure side of the compressor; a temperature sensor to sense a temperature of the outdoor heat exchanger; and a control unit to determine whether a cooling/heating overload operation occurs based on an operation capacity of the compressor, the pressure of refrigerant at the high-pressure side and the temperature of the outdoor heat exchanger, and to control an opening degree of the electric expansion valve to reduce the quantity of liquid refrigerant collected in the receiver during the cooling/heating overload operation.
 2. The air conditioner according to claim 1, wherein the compressor is a Pulse Width Modulation (PWM) type compressor, an operation capacity of which is adjusted according to a loading time for which refrigerant is compressed and an unloading time for which compression of refrigerant stops.
 3. The air conditioner according to claim 1, wherein the sub heat exchanger includes an economizer or super-cooler.
 4. The air conditioner according to claim 3, wherein the electric expansion valve is an Electronic Expansion Valve (EEV) usable with the economizer or the super-cooler.
 5. The air conditioner according to claim 1, wherein the pressure sensor is installed to a discharge pipe of the compressor to sense a high pressure.
 6. The air conditioner according to claim 5, wherein the temperature sensor is installed to a pipe provided at one side of the outdoor heat exchanger to sense a temperature of a heat exchange location of the refrigerant and the water.
 7. The air conditioner according to claim 6, wherein the outdoor heat exchanger functions as a condenser upon a cooling operation, and the temperature sensor senses an exit temperature of the condenser to measure a temperature of the water.
 8. The air conditioner according to claim 6, wherein the outdoor heat exchanger functions as an evaporator upon a heating operation, and the temperature sensor senses an entrance temperature of the evaporator to measure a temperature of the water.
 9. The air conditioner according to claim 7, wherein the control unit determines occurrence of the cooling overload operation if the operation capacity of the compressor is a predetermined capacity or more upon a cooling operation, the high pressure sensed by the pressure sensor is a first predetermined pressure or more and the exit temperature of the condenser sensed by the temperature sensor is a first predetermined temperature or more, and increases the opening degree of the electric expansion valve to bypass the liquid refrigerant inside the receiver to a low-pressure side of the compressor.
 10. The air conditioner according to claim 9, wherein the first predetermined pressure is about 30 kg/cm²G.
 11. The air conditioner according to claim 9, wherein the first predetermined temperature is about 42° C.
 12. The air conditioner according to claim 8, wherein the control unit determines occurrence of the heating overload operation if the operation capacity of the compressor is a predetermined capacity or more upon a heating operation, the high pressure sensed by the pressure sensor is a second predetermined pressure or more and the entrance temperature of the evaporator sensed by the temperature sensor is a second predetermined temperature or more, and increases the opening degree of the electric expansion valve to bypass the liquid refrigerant inside the receiver to a low-pressure side of the compressor.
 13. The air conditioner according to claim 12, wherein the second predetermined pressure is about 35 kg/cm²G.
 14. The air conditioner according to claim 12, wherein the second predetermined temperature is about 30° C.
 15. The air conditioner according to claim 9, wherein the control unit counters a bypass operation time for which the liquid refrigerant inside the receiver is bypassed to the low-pressure side through the electric expansion valve having the increased opening degree, and keeps the electric expansion valve at an original opening degree if the bypass operation time exceeds a predetermined time.
 16. The air conditioner according to claim 9, wherein the pressure sensor senses variation of the high pressure caused by bypassing the liquid refrigerant inside the receiver to the low-pressure side through the electric expansion valve having the increased opening degree, and the control unit keeps the electric expansion valve at an original opening degree if the varied pressure is a predetermined pressure or less.
 17. The air conditioner according to claim 12, wherein the control unit counters a bypass operation time for which the liquid refrigerant inside the receiver is bypassed to the low-pressure side through the electric expansion valve having the increased opening degree, and keeps the electric expansion valve at an original opening degree if the bypass operation time exceeds a predetermined time.
 18. The air conditioner according to claim 12, wherein the pressure sensor senses variation of the high pressure caused by bypassing the liquid refrigerant inside the receiver to the low-pressure side through the electric expansion valve having the increased opening degree, and the control unit keeps the electric expansion valve at an original opening degree if the varied pressure is a predetermined pressure or less.
 19. The air conditioner according to claim 3, further comprising: a solenoid valve is connected to a low-pressure pipe between the economizer and the accumulator and is opened or closed to introduce the heat-exchanged refrigerant from the economizer in the accumulator or the medium-pressure suction hole of the compressor; when the solenoid valve is opened, the refrigerant discharged from the economizer is introduced into the accumulator having a relatively low pressure; when the solenoid valve is closed, the refrigerant discharged from the economizer is introduced into the injection pipe connected to the medium-pressure suction hole of the compressor having a relatively high pressure.
 20. A control method of an air conditioner comprising a compressor to compress refrigerant, an outdoor heat exchanger to perform heat exchange between the refrigerant and water, a receiver to store a part of the heat-exchanged refrigerant to divide the stored refrigerant into gas refrigerant and liquid refrigerant, a sub heat exchanger to perform super-cooling of the liquid refrigerant and an electric expansion valve to bypass the liquid refrigerant, the control method comprising: sensing a pressure of refrigerant discharged from a high-pressure side of the compressor; sensing a temperature of the outdoor heat exchanger; determining whether a cooling/heating overload operation occurs based on an operation capacity of the compressor, the pressure of refrigerant at the high-pressure side and the temperature of the outdoor heat exchanger; and bypassing the liquid refrigerant of the receiver to reduce the quantity of liquid refrigerant collected in the receiver during the cooling/heating overload operation.
 21. The control method according to claim 20, wherein the occurrence of the cooling overload operation is determined if the operation capacity of the compressor is a predetermined capacity or more upon a cooling operation, the pressure of refrigerant at the high-pressure side of the compressor is a first predetermined pressure or more and the temperature of the outdoor heat exchanger is a first predetermined temperature or more.
 22. The control method according to claim 20, wherein the occurrence of the heating overload operation is determined if the operation capacity of the compressor is a predetermined capacity or more upon a heating operation, the pressure of refrigerant at the high-pressure side of the compressor is a second predetermined pressure or more and the temperature of the outdoor heat exchanger is a second predetermined temperature or more.
 23. The control method according to claim 20, wherein the bypass of the liquid refrigerant inside the receiver includes opening the electric expansion valve by a predetermined opening degree to allow the liquid refrigerant inside the receiver to be bypassed to a low-pressure side of the compressor.
 24. The control method according to claim 23, further comprising: checking a bypass operation time for which the liquid refrigerant inside the receiver is bypassed to the low-pressure side through the electric expansion valve having a predetermined opening degree; and keeping the electric expansion valve at an original opening degree if the bypass operation time exceeds a predetermined time.
 25. The control method according to claim 23, further comprising: sensing pressure variation of refrigerant at the high-pressure side caused by bypassing the liquid refrigerant inside the receiver to the low-pressure side through the electric expansion valve having a predetermined opening degree; and keeping the electric expansion valve at an original opening degree if the sensed pressure at the high-pressure side is a predetermined pressure or less. 